The present invention pertains to a force sensitive brake pedal assembly and in particular to a signal generating circuit which provides an electrical signal output according to the force applied to the brake pedal.
Vehicle braking systems employ switches operative to provide an indication of brake pedal depression. These switches are used to activate vehicle brake lights, for example. One type of switch is a mechanical switch actuated whenever the brake pedal is depressed. Another type of switch is actuated by pressure changes in the hydraulic fluid of the vehicle's hydraulic brake system. Another type of mechanical switch includes an operative connection in the mechanical linkage of the vehicle's brake system.
Such prior systems have several disadvantages. Fluid pressure switches occasionally cause leakage in the area where the pressure sensitive switch interfaces with the hydraulic system. Mechanical switches connected in the mechanical linkage increase the magnitude of force required to actuate the brake pedal. Another disadvantage of the mechanical switch systems is they require adjustment when installed and during the life of the system because of linkage wear. Furthermore, a slight force applied to a vehicle brake pedal by the driver through inadvertent resting of the driver's foot on the brake pedal, may cause the associated switch to be actuated even though the brake system has not been energized. As a result, a false indication of braking is provided by the vehicle's brake lights. Additionally, the prior art switches are generally slow acting and switch failure can occur due to electrical contact erosion
Other prior systems include a force sensitive resistor having a variable resistance dependent upon the force applied to the brake pedal. Circuitry responsive t the variable resistance provides an output, or outputs, according to the magnitude of the force applied to the brake. Although the force sensitive resistor an its associated circuitry solve many of the problems of the prior art, the variable resistor does not necessarily maintain constant characteristics over the entire temperature range to which an automobile is typically exposed.